1. Field of the Invention
The present invention relates to saline water processing systems, and particularly to a desalination system utilizing forced air for improved evaporation and condensation performance.
2. Description of the Related Art
Various methods are used for desalination of seawater. One of them is the evaporation/condensation (HD) process. In this method the salt water is evaporated and simultaneously condensed to produce desalinated water. The HD process is based on the fact that air can be mixed with significant quantities of vapor. The amount of vapor able to be carried by air increases with temperature. For example, 1 kg of dry air can carry about 0.5 kg of vapor and about 670 kcal when its temperature increases from 30° C. to 80° C. When the hot, dry air flows in contact with salt water, the air extracts a certain quantity of vapor, which simultaneously cools the hot air via heat transfer so that the air becomes humid. The desalinated water is recovered by maintaining humid air in contact with a cooling surface, causing condensation to occur with some of the vapor mixed with air. Generally, the condensation is carried out in another exchanger, where salt water is preheated by latent heat recovery. An external heat contribution is, thus, necessary to compensate for any heat loss.
Four parameters affect the evaporation process: (a) air pressure, (b) water temperature, (c) water-air contact surface area, and (d) contact time of water with the surrounding air. Evacuation of the desalination unit can improve the evaporation rate, but it is difficult to implement, requiring much consideration of the limitations.
Of course, high salt water temperature increases the water evaporation performance. However, salt scaling problems can limit the allowable temperatures used. Additionally, the temperatures at which a solar system can efficiently perform and the available waste heat must be taken into consideration.
Flashing-water contact surface area can be increased by either increasing flow rate or flashing the water into fine droplets. A limited decrease of the droplets' diameter improves evaporation through improved convective heat transfer at their surface. Moreover, use of forced air convection inside the desalination chamber may improve the evaporation rate. However, studies have shown that natural convection is more preferable, since forced-air convection does not show significant gain in the evaporation rate.
The contact time between the flashed water droplets and the surrounding air is based on the design of the desalination chamber. Heat convection can be improved if the contact time of droplets with the surrounding air is increased. This can be accomplished by increasing the length of the flashing path inside the desalination chamber. For example, conventional systems inject hot salt water vertically downward from the chamber roof. Therefore, the contact time depends on the chamber height, in this case.
For systems that use solar energy as a heat source, the solar collectors are used to heat the salt water. In most instances, the salt water can be directly heated inside the collector. Unfortunately, problems were found due to salt scaling inside the solar collectors. This is exemplary of an open-loop system. In a closed-loop system, the salt water is heated indirectly along a heat exchanger between the collector and desalination loops. One example of a closed-loop system includes a forced solar water heater. Another example utilizes vacuum pressure inside the chamber, which has been shown to greatly improve performance. Additionally, the cost of water production can be reduced using different materials, flow rates and temperatures.
In light of the above, there is still a need in the art of desalination systems to provide a more efficient and improved system and method of extracting desalinated water in current plants. Thus, a solar, water desalination system solving the aforementioned problems is desired.